Magnet valves which are used in connection with highly viscous liquids, in particular in connection with oil burners, are exposed to high demands. Usual conditions are a medium pressure in the range of 30 bar and solenoid temperatures of approximately 165° C. with oils with a viscosity of approximately 75 cSt.
In view of pressures of 30 bar, it is not possible to use media-separated valves, i.e. valves comprising membranes. This means, however, that the valve space, in which the magnet core is moved during the switching of the valve, is filled with a medium and the magnet core is bathed in oil. During the switching procedure, when the magnet core is being attracted, the latter has to displace the oil from the valve space situated on the rear side of the magnet core. Highly viscous media, however, impede the moving of the magnet core, so that the movement is braked. During the attraction of the magnet core, the medium must be able to flow laterally past the magnet core into another portion of the valve space.
In the case of alternating voltage magnets, there is the aggravating factor that voltage peaks and voltage troughs alternate. If the magnet core cannot be quickly attracted during the switching procedure despite the solenoid being activated, so that the working gap is not closed, the solenoid current will consequently increase sharply. This may result in the solenoid being burned out.
In order to achieve better movability of a magnet core in an oil-based environment, it is known from DE 43 43 118 A to equip the magnet core with longitudinal grooves which allow the oil to better flow off from one portion into the other portion of the valve space during the switching procedure. In this process, however, the problem occurs that magnetic material is removed from the magnet core due to providing longitudinal grooves, weakening the magnetic force of the magnet valve. This is why magnet cores are known in the prior art, which have few grooves which are also not particularly deep, so as to avoid the loss of too much magnetic material.
Another solution for the designing of a magnet core is described in DE 10 2010 024 585 A. Here, the heat energy which is produced in the solenoid is supposed to be transferred to the oil to reduce its viscosity.
It is the object of the invention to provide a magnet core for a magnet valve, which allows effortless movability in viscous liquids and is distinguished by a high magnetic force.